There is a recognized need for wide-screen electronic displays in a number of fields, with typical uses ranging from desktop computer applications, to visualization and design software, to diagnostic imaging equipment, to still and motion picture entertainment systems and advertising displays, for example. In a recent paper entitled “DSHARP—A Wide Screen Multi-Projector Display” by Gary K. Starkweather in SID Digest 2003, potential advantages of wide-screen electronic displays for workstation environments are enumerated, including improved productivity and efficiency, minimized “household” chores for desktop organization, improved adaptability to the human visual system, and improved task comprehension.
With existing projection display systems, both film-based and electronic, images can be projected only at limited sizes and aspect ratios. These conventional display sizes are not sufficient to provide large-scale wide-screen display systems based on a single image-forming component. While there have been attempts to fabricate large-scale electronic spatial light modulators, exceeding conventional image frame sizes has proved difficult in practice. Instead, schemes for tiling multiple display systems have been adapted to overcome size and aspect ratio limitations.
Tiling solutions for conventional projection systems have been successfully implemented with various configurations. Tiling arrangements using conventional displays are disclosed in a number of publications, including the following:                “DottyToto: A Measurement Engine for Aligning Multi-projector Display Systems” by Mark Hereld, Ivan R. Judson, and Rick Stevens in Projection Displays IX, Proceedings of SPIE-IS&T Electronic Imaging, Ming H. Wu, editor;        “Immersive Planar Display Using Roughly Aligned Projectors” by Ramesh Raskar, The Office of the Future Group, University of North Carolina at Chapel Hill; and        “Multi-Projector Displays Using Camera-Based Registration” by Ramesh Raskar et al., Department of Computer Science, University of North Carolina at Chapel Hill.        
These and other display tiling solutions operate by attempting precision alignment between projected images from multiple projectors. However, this type of solution is hampered by effects such as slight movement of the display screen, jarring or movement of one or more projection apparatus, expansion due to heat, and imperfections due to projection optics, such as keystoning effects, for example. Moreover, slight color changes in adjacent tiled image sections become readily noticeable, detracting from the intended effect of projection image tiling. Among solutions proposed for tiling projection apparatus with minimal visibility of tile borders are those proposed in U.S. Pat. No. 6,590,621 (Creek et al.) and U.S. Pat. No. 6,513,938 (Kubota et al.).
Tiling has been used for spatial light modulators used in backlighting display applications. For example, U.S. Pat. No. 6,262,696 (Seraphim et al.) discloses a large display panel having a number of precisely aligned LCD display modules arranged as tiles over a backlighting surface; U.S. Pat. No. 5,626,410 (Chambers et al.) discloses tiling of LCD devices in a backlighting display using a fiber optic array for achieving more uniform brightness; U.S. Pat. No. 5,902,030 (Blanchard) discloses a backlighting system using multiple projectors, with a screen outfitted for suitably combining images, such as using Fresnel lens. While these approaches offer some solutions for backlighting systems that form an image on a specially designed, diffusive surface, the apparatus and techniques of these patents are not suitable for front-projection systems.
Tiling approaches have been proposed for printing applications. For example, commonly assigned U.S. Pat. No. 6,580,490 (Wong et al.) discloses the use of multiple tiled LCD spatial light modulators for providing exposure energy to a photosensitive medium over an enlarged two-dimensional area. However, print requirements vary significantly from projection requirements, requiring different solutions for uniformity, resolution, luminous flux, contrast, imaging artifacts, and other image characteristics.
There have been a number of proposed projection systems using multiple spatial light modulators and combining output beams, centered on a single optical axis for projection as a single output beam. For example, commonly-assigned U.S. Pat. No. 6,585,378 (Kurtz et al.) discloses a full-color projection system that employs a separate spatial light modulator in each color path, one each for red, green, and blue light modulation. Modulated light beams from these devices are then overlapped, typically using a polarization beam splitter, an x-cube, or other component as a beam combiner to provide the composite color image. Similarly, U.S. Pat. No. 5,788,352 (Montroy et al.) discloses the use of two LCD spatial light modulators to form overlapping images, providing increased luminance and resolution and improved response time. However, the arrangements disclosed in U.S. Pat. No. 6,585,378 and U.S. Pat. No. 5,788,352 are directed to overlapping of images formed on separate spatial light modulators rather than to tiling images adjacently to increase the size of the projected image.
Thus, it can be seen that tiling arrangements using multiple spatial light modulators have been adapted for a small number of backlit display and print imaging applications. However, projection display apparatus employing LCD spatial light modulators present some significant challenges to tiling implementation. For example, polarization states of incident illumination and modulated light must be accounted for in many types of projection apparatus using these devices. Projection optics must be suitable for projecting a tiled display, where tiles are adjacent, rather than overlapping as in the apparatus of U.S. Pat. No. 6,585,378 and U.S. Pat. No. 5,788,352.